Thread: My stropping technique.

Originally Posted by BKratchmer

There needs to be a certain amount of force to bend the steel. Since this cannot come from downward friction, a critical momentum needs to be met to really effectively strop. It's why you buff with rouge on a large, fast wheel- it will cut so slowly otherwise that it would take exponentially longer to get the same effect. No more pressure, just more speed.

There is NO physical support for this. Momentum=mass dot velocity (M=mdotV), or simplified, mass times speed (M=ms). Friction=normal times coefficient of friction (Fr=N(mu)). There is no reason to assume friction depends on speed. The friction on the blade edge is constant (assuming your downward (normal) force is constant)

If you were to supply an initial impulse there might be a critical momentum one would need to complete a stropping stroke, but since we are providing a constant force input, there is no "critical" momentum we need to achieve. This would be the same as accelerating a car to say 30 mph then letting it coast to a stop. In order to say, have that car travel 200m, one would need to have a critical momentum at the end of the acceleration. However, if you are going to supply a constant force (ie not coast) it would be a simple matter to travel 200m, you could have a momentum of 20kgm/s or 50 kgm/s it doesn't matter.

The reason you cut on a large, fast wheel is this. Distance = (pi)*d*w*t, or pi times diameter of the wheel times angular velocity times time. As such:
A 2" wheel, 2000rpm, 1 min= pi*d*w*t= 3*2*2000 = about 12000" a min.
A 4" wheel, 2000rpm, 1 min= pi*d*w*t= 3*4*2000 = about 24000" a min.
A 2" wheel, 4000rpm, 1 min= pi*d*w*t= 3*2*4000 = about 24000" a min.
Thus one can see, the bigger and faster a wheel, the more tangential distance is covered. The frictional force depends only on the normal force and coeffecient of friction, and the distance covered. Stropping faster allows you to cover more distance in a minute, but 60 laps in a minute or 60 laps in 5 mins should have the same effect.